Paper No: 4 Environmental Geology Module: 07 Glaciers Development Team Prof. R.K. Kohli Principal Investigator & Prof. V.K. Garg & Prof. Ashok Dhawan Co- Principal Investigator Central University of Punjab, Bathinda Prof. R. Baskar, Guru Jambheshwar University of Paper Coordinator Science and Technology, Hisar Dr Anita Singh, Central University of Jammu, Jammu Content Writer Dr. Somvir Bajar, Central University of Haryana, Content Reviewer Dr B W Pandey, Department of Geography, Delhi University, Delhi Anchor Institute Central University of Punjab 1 Environmental Geology Environmental Sciences Glaciers Description of Module Subject Name Environmental Sciences Paper Name Environmental Geology Module Glaciers Name/Title Module Id EVS/EG-IV/07 Pre-requisites 1. Understand glacier and differentiate the different types of glaciers 2. Describe glacier formation and glacier movement Objectives 3. Understand glacial budget and mass balance 4. To study different types of glacier landforms Keywords Glacier, Calving, Ablation, Accumulation 2 Environmental Geology Environmental Sciences Glaciers Module 07: Glaciers Objectives 5. Understand glacier and differentiate the different types of glaciers 6. Describe glacier formation and glacier movement 7. Understand glacial budget and mass balance 8. To study different types of glacier landforms 7.1 Glacier Glacier is a mass of surface ice on land and formed by accumulation of snow. Glaciers flow downhill under gravity due to its own weight. Glaciers are maintained by accumulation of now and melting of ice. The melted ice discharged into the lakes or the sea. Glaciers grow and shrink in response to the climate change. Meier (1974) provided a definition of a glacier: “A glacier may be defined as a large mass of perennial ice that originates on land by the recrystallization of snow or other forms of solid precipitation and that shows evidence of past or present flow. The definition is not precise, because exact limits for the terms large, perennial, and flow cannot be set. Except in terms of size, a small snow patch that persists for more than one season is hydrologically indistinguishable from a true glacier. One international group has recommended that all persisting snow and ice masses larger than 0.1 square kilometers (about 0.04 square mile) be counted as glaciers. Hence, in the absence of an agreed-upon upper size limit for glaciers, a body of ice as large as the Antarctic Ice Sheet (slightly smaller than the conterminous United States and Europe combined) could properly be considered a glacier.” Important facts about glaciers: Glaciers store about 75% of the world’s fresh water. Glacier ice crystals can grow to be as large as baseball. 3 Environmental Geology Environmental Sciences Glaciers The largest glacier in the world is the Lambert-Fisher glacier in Antartica. Ice is a mineral as it possesses a definite chemical composition and atomic structure, and non- metallic inorganic and crystalline (Drewry, 1986, p.1). Selected mechanical and thermal properties of ice are shown in Table 1 (Drewry, 1986, p.2) Property Units Symbol Quantity Mechanical -3 Density Kg m ρi 920 Young’s module GN m-2 E 9.10 -2 Yield strength MN m σy 85.0 -3/2 Fracture toughness GN m KC 0.2 -2 Toughness KJ m GC 0.003 Creep activation J mol-2 Q 6.07×104 energy Flow law constant Pa-3 S-1 B 8.75×10-13 Pressure melting Deg Pa-1 -0.7×10-7 coefficient Thermal Melting temperature K 273.1 -1 -2 Thermal W m Deg Ki 2.51 conductivity 2 -1 -6 Thermal diffusivity m s Ki 1.33×10 Heat Capacity J mol-1 Deg-1 37.7 4 Environmental Geology Environmental Sciences Glaciers Latent heat (fusion) KJ Kg-1 00 C 334 -100 C 285 -200 C 241 Sources of water in glaciers and Ice sheets a) Surface Melting b) Dissipation of mechanical heat c) Geothermal heat d) Groundwater flow and surface runoff e) Liquid precipitation The blue color of glacial ice: Snowfall covers the surface and forms a layer of snow. Every year, snowfall makes layers and create pressure on the older layer beneath. As the time pass, the low-density snow transformed into much denser solid ice. Due to compaction, pressure melting (as ice melts at 00C at atmospheric pressure, but under high pressure melts at a lower temperature) and refreezing reduce the air in the frozen mass and increase materials density. As, the density of ice increases, it reflects the more short wavelength of light, i.e. blue part of the spectrum. (Source- James Petersen, 2011, p. 394). Area covered by glaciers Table 1: Approximate worldwide area covered by glaciers (Source- Global Glaciers Changes: facts and figures 2008; ttps://nsidc.org/cryosphere/glaciers/questions/located.html) New Guinea 3 square kilometers (1.16 square miles ) Africa 6 square kilometers (2.23 square miles ) New Zealand 1,600 square kilometers (617 square miles) 5 Environmental Geology Environmental Sciences Glaciers Scandinavia 2,490 square kilometers (1,135 square miles) Central Europe 3,785 square kilometers (1,416 square miles) South America 25,500 square kilometers (9,846 square miles) Northern Asia 59,600 square kilometers (23,012 square miles) Antarctica (not including the main ice sheets) 77,000 square kilometers (29,730 square miles) Central Asia 114,800 square kilometers (44,325 square miles) North America 124,000 square kilometers (47,877 square miles) Arctic Islands (not including the Greenland 275,500 square kilometers (106,371 square Ice Sheet) miles) 7.2 Glacier formation Glaciers are masses of flowing ice that accumulated over a period of time and the snowfall is more than the melting of ice. The formation of glaciers starts when snow remains in the same area for a year and when enough snow accumulate and transform into ice. When a snow falls, its hexagonal ice crystal and called snowflakes, having a density of about 0.1 grams per cubic centimeter (0.06 oz/in3.) as shown in image 1. 6 Environmental Geology Environmental Sciences Glaciers Image- 1 Formation of glacial ice Each year a new layer of snow is added and this layer compresses the older layer. The snowflakes are transformed into granular snow by melting and refreezing. With time, the grains grow and the air pockets between them decrease and become more compact as well as an increase in density. Due to the melting, refreezing, and pressure caused by new snowfall, the granular snow is converted into firn. The firn formation takes place after about 2 winters. Over a period of time and due to pressure, partial melting, and refreezing, the ferns grow together into larger interlocked ice crystals. When the ice crystals are more compacted and very little amount of airspace left between them, they are called glacial ice. The firn is about two-thirds as dense as water but the density of glacial ice is becoming 0.9 grams per cubic centimeter (0.52 oz/in3.). So, from snow into glacial ice, there is a lot of transformation (as shown in fig. 1) and increase in density. Glaciers are formed when snow remains in one place for a longer time and face many transformations. Glaciers size varies from a small football field to hundreds of kilometers long area. Glaciers are mostly present in Polar Regions like Antarctica, Greenland, and the Canadian Arctic, and occupy nearly 10% of the world’s total Land area (Source- NSIDC glaciers). Accumulation and ablation are two most important terms in the formation of glaciers. Accumulation area is the area where snowfall is accumulated (usually 7 Environmental Geology Environmental Sciences Glaciers higher elevation) and ablation area (usually lower altitude) where melting and evaporation takes place. Mostly the accumulation takes place in winter and ablation part takes place in summer. The glacier is in equilibrium when the snowfall equals snowmelt, when this equilibrium is disturbed either by excessive snowfall (called advances) or by excessive melting (called retreats). The glacial system is controlled by frozen precipitation and freezing temperatures. 7.3 Glacier movement Glaciers flow downhill due to the gravitational force generated by their own weight. Glacial velocity depends upon the thickness of glacier, temperature, bedrock, and gradient. Movement takes place by one or combination of following three processes (Source- http://geomorphology.org.uk/sites/default/files/intro_to_glaciers.pdf ) 1) Internal deformation: Glaciers have ice crystals and when there is slippage within or between ice crystals leads to glacier movement. The base having highest pressure and maximum deformation takes place at the base. 2) Basal sliding: This involves the sliding of a glacier over its rocky base. The basal sliding is of three types- basal slip, enhanced basal slip, and regelation slip. 3) Bed deformation: This is movement accomplished by the deformation of soft sediment or weak rock beneath a glacier. A study conducted on the glacier movement in 1948 on the Jungfraufirn glacier, found that the ice near the surface is rigid and brittle. When the glacier flows rapidly at a location, friction creates giant cracks called crevasse (image 2). Moraine is another common feature of the glacier when it pushes or carries rocky debris as it moves. There are different types of moraine-like medial moraine (run down the middle of the glacier), lateral (run down along the edges) and terminus moraine (found at the terminus or snout of a glacier). Below the brittle zone, due to weight of the overlaying ice, the ice start flowing instead of breaking. This zone is called plastic zone and ice flow in this zone. 8 Environmental Geology Environmental Sciences Glaciers Image-2 Crevasse on the Easton Glacier in the North Cascades (source- http://opengeology.org/textbook/14-glaciers/) 7.4 Types of glaciers Different type of glaciers Alpine glaciers: Alpine glaciers are found in mountain terrain and where the precipitation and temperature conditions present due to high elevation.